Filters which employ a filter medium and a filtration aid in order to avoid blinding of the filter medium and thereby to extend the cycle time between backwashing procedures, generally operate on the principle that inlet fluid serve to stir up the filtration aid which then becomes deposited on the filter medium. The latter may be a fabric the form of a bag or sleeve supported over a framework. When the filter is switched off for a period of time, the mixture of dirt and filtration aid, which is typically diatomaceous earth, falls off the filter medium and becomes deposited on the bottom of the filter container.
When the filter is re-started the turbulence of liquid in the filter tank causes the mixture of filter aid and dirt to lift off the bottom of the container and become re-deposited on the filter medium.
It is important that the filter aid become reasonably evenly deposited over the entire surface area of the filter medium and, where the filter medium comprises a large number of tubular sleeves supported on frames therefor wherein the sleeves all extend parallel to each other, generally in a substantially vertical direction, the distribution of the filtration aid may be somewhat uneven.
It is the object of this invention to provide a liquid filter in which the distribution of filtration aid deposited on the bottom of a filter container during off periods is effectively mixed with incoming liquid to be filtered so as to enhance the distribution of the filtration aid over the surface area of the filter medium in the filter.